This application claims priority to German Patent Application No. 10 2006 016 761.9, filed on Apr. 10, 2006.
A transmitter can be used to transmit information using a data signal via a physical transmission channel in a communication system. By way of example, the physical transmission channel may be a cable or, as in the example of a mobile radio system, a radio channel. With the radio channel, the transmission power of the transmitter corresponds to a signal level for the outgoing data signal.
Many mobile radio systems require that the data signals be turned on and off with a high degree of precision. These mobile radio systems include systems such as the Global System for Mobile Communication (GSM), the Universal Mobile Telecommunication System (UMTS), Bluetooth and the Wireless Local Area Network (WLAN). With these systems, specifications for the output power and the permitted spectral transmissions are defined by standards such as the GSM standard, for example, as in 3GPP TS 45.005.
In order to provide a transmitter that can operate in accordance with multiple communication standards and transmit signals using different frequency bands at varying power levels and allowed spectral emissions, the power level at the output of the transmitter must be controlled with a high level of precision. Various approaches have been used to control the power level. One approach is to use a closed power loop wherein the power level at an output of the transmitter is measured and compared to a desired power level to regulate the power level of an outgoing signal.
Another approach is to use a Cartesian loop to perform a demodulation of a sample of the outgoing signal to reconstruct an Inphase signal and a Quadrature signal to control the linearity of the transmission path.
Still another approach is to use a polar loop as a feedback loop in an amplitude path of a polar transmitter to ensure the linearity of an amplitude component of the transmission signal.
These approaches have been used in transmitters for narrow band applications. Because data rates in communication systems have been increasing, wideband transmitter usage is becoming more common. As a result, high linearity and output power are becoming more difficult to achieve.
For these and other reasons, there is a need for the present invention.